(a) Field of the Invention
The present invention relates to a siloxane-modified polyamideimide resin composition, an adhesive film, an adhesive sheet, a CSP board and a semiconductor device produced by using the composition.
The present invention further relates to a siloxane-modified polyamideimide resin useful for the siloxane-modified polyamideimide resin composition, and to varnish containing the siloxane-modified polyamideimide resin.
(b) Description of the Related Art
Polyamideimide resins are mainly used for wire coating (heat-resistant enamel wire) because they are excellent in electrical properties, heat resistance, mechanical properties and abrasion resistance. However, the high boiling solvents that are usually used for the production of polyamideimide resins have hindered forming film or sheet of polyamideimide resins. For example, they need time-consuming drying at low temperatures of 150.degree. C. or lower, and the resulting film or sheet still contains at least 10% by weight of residual volatile matters. Even by drying at high temperatures above 150.degree. C., it is difficult to produce sheets of above 100 .mu.m thick containing not more than 5% by weight of residual volatile matters. Further, when resin compositions comprising polyamideimide resins and thermosetting resin ingredients are dried at high temperatures to produce sheets, thermal cure proceeds excessively, to make the production of B-stage sheets difficult.
An application of polyamideimide resins is the production of interlaminar adhesive films for wiring boards, which are films or sheets formed by applying resin compositions comprising polyamideimide resins and thermosetting resin ingredients on appropriate substrates. The desirable content of residual volatile matters in such films and sheets is 5% by weight or less, preferably 1% by weight or less. In films and sheets containing much volatile matters, voids or bubbles may be produced during processing with heat, such as press, bonding with heat and pressure or lamination, or thermal after-cure, which deteriorate insulating properties. In addition, such films and sheets must preserve their flowability to adhere to the substrates of printed circuit boards or to fill the depressions of the thickness of the copper foil made in the circuits. Therefore, drying of coating must be carried out at low temperatures so as not to cause thermal cure. It is desirable to decrease the residual volatile matters in sheets of any thickness, for example thick sheets above 100 .mu.m thick. It is also desirable that the films or sheets of the resin compositions strongly adhere to the substrates.
In LSI-packaging technology, CSP's (chip-size-packages) have been popularized, which permit reducing the mounting area of LSI to chip sizes. CSP's have short wiring length, and produce little inductance. Therefore, they can speed up and improve the performances of LSI's, and are advantageously applied in recent cellar telephones and video cameras, and further in the DRAM of personal computers.
There are various types of CSP's, including the wire-bonding type, the ceramics type, the through-hole type and the .mu.BGA type. Wire-bonding-type CSP's are produced by connecting chips to polyimide wiring boards by wire bonding followed by sealing with resins. CSP's of this type have simple structures and can be produced by modification of the conventional BGA techniques, and are expected to be the main current of CSP's with up to 100 small pins.
For example, CSP boards for wire-bonding type are produced by initially making through-holes, such as solder ball holes, in polyimide substrates coated with adhesives which can adhere to copper foil on heating, followed by lamination of copper foil by pressing or the like, circuit forming and gold plating. As the adhesives for bonding polyimide substrates and copper foil, epoxy resins, polyamic acids and mixtures of polyamic acids and bismaleimides have been used, while polyamideimide resins have been used mainly as wire coating materials because of the excellent electrical properties, heat resistance, mechanical properties and abrasion resistance.
As CSP's have been downsized and the number of pins has increased, the circuit of CSP boards has become finer, requiring heat resistant adhesives which adhere to copper more strongly. Conventional epoxy resin adhesives have poor resistance against wire-bonding or solder reflow owing to lack of heat resistance. Polyamic acids and mixtures thereof with bismaleimides have excellent heat resistance, but need high curing temperatures of 300 to 400.degree. C., and their adhesion to copper foil or molded resin is insufficient.
An object of the present invention is to provide a siloxane-modified polyamideimide resin composition, which can form films containing little residual volatile matters, has high adhesion strength, appropriate flowability and superior heat resistance, strongly adheres to polyimide base layer and copper foil, exhibits excellent resistance to PCT (pressure cooker test) and, therefore, is useful for the production of interlaminar adhesive film for wiring boards.
Another object of the present invention is to provide an adhesive film, an adhesive sheet, a CSP board and a semiconductor device, which are produced by using the siloxane-modified polyamideimide resin composition.
Another object of the present invention is to provide a siloxane-modified polyamideimide resin useful for the preparation of the siloxane-modified polyamideimide resin composition.
Another object of the present invention is to provide a varnish containing the siloxane-modified polyamideimide resin.
Polyamideimide resins are typically produced by the isocyanate method comprising the reaction of trimellitic anhydride with aromatic diisocyanates, or by the acid chloride method comprising the reaction of aromatic diamines with trimellitic chloride followed by reaction with aromatic diisocyanates. The kinds and properties of the polyamideimide resins obtainable by the diisocyanate method are limited owing to the scarcity of the kinds of commercially available industrial aromatic diisocyanates. On the other hand, the acid chloride method needs a purification process for removing the by-product HCl, and therefore is disadvantageously costly. Japanese Patent Application Unexamined Publication No. 3-181511 discloses the production of polyamideimide resins by a two-step method comprising the reaction of aromatic tricarboxylic anhydrides with excess diamines having ether bonds, followed by reaction with diisocyanates. Japanese Patent Application Unexamined Publication No. 4-182466 discloses the production of diimidodicarboxylic acids of high purity by the reaction of aromatic diamines with trimellitic anhydride. If combined with the reaction of the product diimidodicarboxylic acids with diisocyanates, this method may enable easy production of substantially by-product-free polyamideimide resins of high molecular weights from various kinds of diamines, since it does not produce the by-product HCl that is formed in the acid chloride method.
Polydimethylsiloxanes consist of highly ionic, cohesive main chains and nonionic and less cohesive side chains, and when there is no action except the interaction between polymers, they are known to have helical structure, with the siloxane bonds directed inward. It is also known that introducing siloxane structures into polymers enlarges the space occupied by polymer molecules due to the helical structure of the siloxane parts, thereby increasing the gas permeability of the polymers. Siloxane structures are also expected to improve resin properties including elasticity and flexibility because they are scarcely interactive each other in spite of their vigorous vibration with heat. If siloxane structures can be introduced into inherently heat resistant polyamideimide resins by the industrially advantageous isocyanate method, it will be possible to produce heat resistant polymers of various properties and improve the drying efficiency of polyamideimide resins, which are usually produced by using high boiling solvents. However, there have been proposed no method of producing high molecular weight polymers.
The method disclosed in Japanese Patent Application Unexamined Publication No. 3-181511, wherein aromatic tricarboxylic anhydrides are allowed to react with excess diamines having ether bonds followed by reaction with diisocyanates, needs dehydration agents because the first reaction stage requires not only the reaction of acid anhydrides with amino groups but also the reaction of carboxylic acid with amino groups. Therefore, oligomerization occurs even in the first reaction stage, and, in the second reaction stage, various competing reactions occur between oligomers of different molecular weights and diisocyanates, to form by-products. It is therefore impossible to produce polyamideimide resins having sufficiently high molecular weight. If the diimidodicarboxylic acids produced by the method disclosed in Japanese Patent Application Unexamined Publication No. 4-182466 are allowed to react with diisocyanates, polyamideimides of desired properties will be obtainable by using various commercial aromatic diamines, and the absence of the by-product HCl formed in the acid chloride method will facilitate the production procedure. However, as taught in Japanese Patent Application Unexamined Publication No. 4-182466, the diimidodicarboxylic acids produced from diamines having two or less aromatic rings are insoluble in the solvents used for synthesis, and must be filtered previous to succeeding reactions, causing a costly increase of filtration or purification steps. Another drawback is that the purified diimidodicarboxylic acids have low solubility, so that the molecular weights of the reaction products thereof with aromatic diisocyanates are too low to produce film from varnish thereof.
According to an improved method, high molecular weight polyamideimide resins are produced by allowing diamines having three or more aromatic rings with trimellitic anhydride in the coexistence of aprotic polar solvents and aromatic hydrocarbons azeotropic with water, to remove the by-product water by distillation, and then allowing the obtained aromatic diimidodicarboxylic acids with diisocyanates. However, when the diamines are partially replaced by siloxanediamines, this method could not produce siloxane-modified polyamideimide resins having sufficiently high molecular weights.
To solve the problem, we have studied to provide a method whereby high molecular weight siloxane-modified polyamideimide resins can be produced without filtration steps, and have completed the present invention.